Diet and forage quality of intermediate wheatgrass managed under continuous and short-duration grazing
M.L. NELSON, J.W. FINLEY, D.L. SCARNECCHU, AND S.M. PARISH
AhStUCt
Diet quality and forage
quality were determined under lortdlw8tioa8ndcontinaou8~of
iIlwmd8te
WhaQlnlm
(~brqpprouriidanrarlitlm)in~ygizlng~in19115~d
lw16. lhe short-duration lllly waedivided into 8 e&units grazed
eequentially for 3 dayr each. Ss crowbred heifers and 2 eaopbageally fietuhhd steere were randomly aedgned to uch grazing
treatment. Aoimab were wdghed and fecal mmplm, pasture mmplea, and diet (aopbageal masticate) samplea were collected in
each of tbe three 24day per&de. In vitro organic matter diup
peuence (IVOMD) of steer dkta uoda shortduration grezing
declinedlineariyavoaperfodsofbothyeusendacroesdays
within periods in 1986. Crude protein content of steer diets under
ehortduration grazing dedined quadratically acroes periodn in
MM. Crude protein and IVOMD content of steer dieto under
continuous grazing dedined linearly in 1985. The effects of 4
mataritia of intermediate wbea@rase on d@tbUty
and mminal
kbetice were compared in a 4 X 4 Latin quare dedgn with 4
rumhully and abomasally w
crossbred wethere. Organic
matter intake and diptibility,
in eku rate and extent of NDF
digatiotb Uq&l passage rate and partkubte man fhbwing from
ment models to predict animal, plant, and economic performance
of alternative grazing systems. Therefore, objectives of these trials
were to determine seasonal changes in diet composition and in vivo
organic matter digestibility under short duration and continuous
grazing and determine effects of intermediate wheatgrass maturity
on intake, digestibility, in situ rate of digestion and fluid and
particulate passage rates.
Materials and Methods
Grazing Trials
Two 72day grazing trials were conducted on part of a 48-ha
intermediate wheatgrass (Agropyron intermedium] pasture in antral Washington. The study area was described in detail by Pierson
and Scamecchia (1987).The area was divided by ocular and stratigraphic estimates of equivalent standing crop into 2 units, 1 for
SDG and 1 for continuous grazing. The SDG unit was further
subdivided into 8 subunits. Short duration grazed subunits averaged .35 ha in both years and the continuously grazed unit was 3.76
and 3.54 ha in 1985and 1986,respectively.
Six crossbred pregnant heifers (average weight 356 kg) and 2
crossbred steers with esophageal fistulas (averageweight 326 kg in
tbeN3ncndcereucdliawly~hrenucdfo~ge~~.Thac
d8ta suggested that effects offorage maturity or period of grazing 1985, 273 kg in 1986) were randomly assigned to each of the 2
bad similar effects 011diet quality and forage quality. However, grazing systems. Animals in the continuous grazing treatment
grazed the entire unit for 72 days. Initial stocking density on the
dictq~llndcrrbort_duntion~gIbodcelined~orrdlyr
continuous unit was .8 and .9 AU/ ha and on the SDG unit was 1.I
withinsubpaib.
and 1.1 AU/ha for 1985 and 1986, respectively. Animals in the
Key Wards: Agropyron iidcnrsormum,fora~beef&tle,Weth~
SIX treatment grazed each subunit for 3 days; then, all animals
dbatim,
Fee
r8tee
were moved into the next subunit. Therefore, subunits were grazed
Because the demand for grazing is projected to increase (Reid for 3 days followed by 21 days of rest in each of the 3 periods. Initial
and Klopfcnstein 1983), management systems must be developed stocking density for the SDG subunits ranged from 6.9 to 9.9
to increase range and pasture productivity and cff%ziency.Maturity AU/ ha in 1985and 6.2 to 11.7 AU/ha in 1986. Stocking variable
of forage plants (Brady 1973)and type of grazing system (Pitt 1986) terminology was according to Scamecchia and Kothmann (1982)
affect the chemical composition of forage. As forage plants and animal-unit-equivalents were based on the model of Scamecmature, crude protein content and digestibility decrease and fiber chia and Gaskins (1987). The 72day studies were conducted from
fraction concentration increases. Dietary chemical composition 18 May to 29 July 1985 and 23 May to 3 Aug. 1986. Mineral
and increased forage maturity alter rate of passage (Bull et al. 1979) supplement (50% dicalcium phosphate and 50% trace mineralized
and fermentation kinetics (Mertens 1977).
salt’) was provided ad libitum.
Twenty-five randomly distributed .5 m2 plots were clipped to
Short duration grazing (SDG) may allow greater stocking rates
than continuous grazing (Heitschmidt et al. 1982b, Jung et al. ground level before and after grazing in each subunit through the 3
1985).This could be due to increased forage quality and quantity rotations to estimate standing crop. In the continuously grazed
or efficiency of harvest (Heitschmidt et al. 1982b).However, SDG unit, standing crop was estimated by clipping, to ground level, 40
has, in some studies, been shown to have no effect on animal weight randomly distributed .5 m2 plots at 7day intervals in 1985 and
gain (Heitschmidt et al. 1982a.Jung et al. 1985).Chemical compo- 24day intervals in 1986.
In 1985,heifers were weighed on day 1,2,7,8,9,31,32,33,55,
sition of diet (esophageal masticate) may be the most sensitive
measure of change due to grazing management. However, compo- 56,57,71, and 72. Esophageal masticate samples were collected on
sition of forage selected by animals grazing a cool-season forage day 7 to 12in each period alternating between a.m. and p.m. times
under continuous and SDG systems as forage mature4 has not been of grazing without a previous fast to avoid fasting-induced, seIecreported. These data are needed to adequately evaluate the grazing tive grazing (Siiahmed et al. 1977).Esophageal masticate samples
system by forage maturity interactions and to be used in manage- were frozen (-20” C) until they were lyophilized. Esophageal masticate samples were composited (w/w) by steer, within day 7 to 9
AuthorsUCurirunt professor and pduate ashant, Department of Animal and within day 10to 12, representing subunits 3 and 4 underSDG,
Scimaq associntc rofessor, Dcputmcnt of Natural Resource scicnca; and anaociate p+amr, CcllL gc of VeteliMry Malick. Wuhington state univenity. Fullnun 99164.
Scicntifii paper 7845, a&Se of Apiculturr Md Home Emlomics. wMllingtoll
State Univemitv. R-h
cowhctd uder Proiect 0713.
Muldpt
iazptcd 9 Much 1989.
474
‘97%NaCl,
.002% Se, .014% Co, .OlS%I .032% Cu. 24% Fe, .31% Mn, ~56%Zn.
JOURNAL
OF RANGE MANAQEMENT
42(6), November
1989
in each period. Fecal grab samples from heifers were collected on
day 7 and 8 in each period, and frozen until subsequent analyses.
Subsamples were taken from pasture plots.
In 1986,heifers were weighed on day 1,2,7,8,3 1,32,55,56,71,
and 72. Esophageal masticate samples were collected on day 7,8,
and 9 representing subunit 3 under SDG, ineach period alternating
between a.m. and p.m. collections. Esophageal masticate samples
were froxen (-200 C) until they were lyophiied. Fecal grab samples from heifers were colIected on day 7 and 8 in each period, and
frozen until subsequent analyses. Subsamples were taken from
pasture plots.
Fecal grab samples were ovendried at 50“ C and cornposited
(w/w) by animal. Pasture samples were oven-dried at 500 C. All
samples were ground through a l-mm screen in a Wiley mill.
Chemical analyses of pasture samples and esophageal masticate
samples included crude protein (CP) by macro-Kjeldahl (AOAC
1984), neutral detergent fiber (NDF), acid detergent fiber (ADF)
and acid detergent lignin (ADL) according to Goering and Van
Soest (1970) and in vitro organic matter digestibility (IVOMD) by
the Moore modiication (Harris 1970)of Tilley and Terry (1%3).
Crude protein contents of esophageal masticate were corrected for
urea-N content. Urea-N in esophageal masticate was measured by
extracting soluble N in 10% Burrough’s buffer (Burroughs et al.
1950) at 37” C for 1 hour and measuring ammonia-N by the
phenol-hypochlorite method (Weatherbum 1%7). All chemical
analyses are reported as a percentage of organic matter. Ash-free
indigestible acid detergent fiber (IADF) was measured in fecal and
esophageal samples according to Nelson et al. (1985). A preliminary study (ML. Nelson, unpublished data) showed no effect
(p>.l) of sampling day within collection period on fecal IADF
content of grazing animals. Therefore, animals were assumed to be
in steady state conditions. In vivo forage organic matter digestibility (in vivo OMD) was calculated using IADF as the internal
marker (Harris 1970).
MlatlollTrlaI
Intermediate wheatgrass was harvested from an adjacent ungrazed portion of the 48-ha seeded field used for the graxing
studies. Forage was harvested with a rotary mower and sun-cured
at 4 stages of maturity (late boot stage, full head, mature and post
ripe) on 26 May, 19 June, 13 July, and 6 Aug. 1985.
Four ruminally and abomasally fistulated crossbred wethers
(average weight 82 kg) were randomly allotted to a 4 X 4 Latin
square design. Dietary treatments were the 4 stages of maturity of
intermediate wheatgrass. Two cells of maturity 1forage were missTabkl.
ing because we did not harvest enough forage. Wethers were fed, in
amounts to allow 20% feed refusals (orts), twice daily at 0700 and
1900. Mineral supplement (50% diilcium phosphate and 50%
trace mineralized salt’) was provided ad libitum.
Animals were housed in a temperature-controlled, continuously
lighted room. Periods were 11 days in duration, which included
day 1 through 7 for diet adaptations and day 8 through 11 for
collection of ruminal, abomasal, and fecal samples. Feed intake
was determined as feed offered, corrected for arts from day 6
through 9.
Rate and extent of digestion of neutral detergent fiber (NDF) of
the 4 diets was determined using 5 X 10cm dacron bags2(pore size
52 f 16 p m). About 2 g of forage, which was previously ground
through a 1-mm screen in a Wiley Mii, was placed in each dacron
bag. Bags containing the same forage that each sheep was fed were
suspended in the rumen at 0708 on day 8. Duplicate bags were
removed from each sheep at 4,8,12,24,48,72, and 96 hours of
incubation. Bags, after removal from the rumen, were frozen (-Up
C) until subsequent analysis. Bags were thawed, rinsed with water,
and the residue remaining in each bag was quantitatively transferred for NDF analysis.
Rate of liquid passage was determined using a 5-g dose of cobalt
lithium ethylenediaminetetraacetic acid (CoLiEDTA) synthesized
according to Uden et al. (1980). Rate of particulate passas was
determined using a 15-g dose of ytterbium (Yb) labeled forage
prepared according to Goetsch and Galyean (1983). Ytterbiumlabeled forage contained an average of 8.4 mg Yb/ g. An aliquot of
forage of each maturity was ytterbium labeled so that labeled
forage and the diet of each sheep within a period were the same.
Markers in gelatin capsules were administered into the rumen
simultaneously with the insertion of dacron bags. Ruminal contents, samples at 0,4,8, 12,24,48,72, and 96 hours after dosing,
were obtained using a 15-mm diameter rubber tube with a wire
running through the center which was attached to a rubber
stopper. The tube was inserted through the ruminal strata and then
sealed. Each collection was a composite of samples from different
sites (ventral sac, dorsal sac, and reticulum) in the reticula-rumen.
Composite samples were strained through cheesecloth to separate
liquid from particulate fractions. Contents of the abomasum were
sampled at 1000,1300,1600, and 1908 on days 8,9,18, and 11 in
each period, respectively.
‘RIO2 Muvclaii White, Erlmgcr, Slumgut & Co., Inc.. New York, NY.
Qmntityandqdtyofinte-whatgruaun&rsbortda~t~oeandeoounmmsgruing.
24!29
1985;Period
17-22
2
11-16
3
2b31
1986;Period
22-24
2
3
1618
MaY
Jun
Jul
fiY
JUn
Jill
8.3
6.3
4.3
9.2
6.2
3.9
0.4
Standing
crop,
kg/ unitb %+j
In
vitro OM
digcstibiitv.
Standing crop, g/ rn%
3503
77.6
125.6
2847
72.8
102.1
1732
65.2
62.1
3240
70.3
116.1
3184
65.3
114.1
%
72.6
&!
8.5
Continuour gmzing
Crude protein, 9%of or@
In vitro OM diitibilitY, Bbd
Standing crop, kg/ unit
Standing crop, g/m%
9.1
75.8
3504
93.2
6.2
74.3
2460
65.4
3.9
68.6
1352
36.0
9.6
66.7
3199
90.3
5.6
63.8
3397
95.9
6:*3
0.4
1.1
700
18.4
Item
Shortduration grazing
Crude protein,$ of organic matter
(OW
30th
84.5
SEW
staluhrd errorof the man.
ulcar effect of period (K.05).
%lau effect of riod (K.01).
%fkct of year ( E .01).
JOURNAL OF RANGE MANAGEMENT 42(6), November 1989
475
Tabk2. C~podtion
ofsteerdkk
(amphaged masticate)under shortduratIon and conthmo~~ grazing, 1WrS.
-Period
24-26’
May
Item
I
-Period
21-29
WY
2
17-19
JUn
20-22
Jun
-Period
11-13
Jill
‘I
14-16
Jul
SEMb
% of Organic Matter
1; vitro OM digestibiitfl
13.4
72.1
12.3
72.5
12.0
70.2
10.9
70.9
8.5
61.0
Neutral detergent fibcf
Acid detergent fibef
Acid detergent lignin
52.2
30.9
6.9
55.6
31.6
5.9
52.2
29.6
4.5
53.5
30.9
6.6
Continuous grazing
CNdt protein’
In vitro OM digestibility’
Neutral detergent fiber
Acid detergent libef
Acid detergent lignin
13.4
69.3
53.9
30.8
8.3
13.0
74.6
52.4
29.6
1.3
10.3
66.4
60.1
33.8
6.8
8.9
61.7
57.7
32.9
7.6
59.1
38.0
9.6
7.5
60.1
58.8
36.5
9.1
&
7.3
55.5
60.1
31.5
9.6
6.3
58.0
60.9
38.6
12.1
k9
6:2
2.7
1.2
0.5
2.3
1.6
tUndcr shortduration grazing, fit data under each period WCICOIIsubunit 3 and second dates on subunit 4.
Standard error of the mean cabxdated from &ccr by period by day; n=2.
xiir
cffcct of Lwiod IJK.09.
%ii CtTectof -&ad @c.osj.
‘Quadratic CtTcctof period (fc.10).
Quadmtic effect of period (X05).
Samples of feed, orts, feces, abomasal contents, and ruminal
contents were dried at 500 C in a forced-air oven. Samples of feed,
orts, feces, and abomasal contents were ground through a‘Wiley
Mill (l-mm screen). Samples were composited (w/w) by wether
within period. Chemical composition of feed, orts, abomasal contents and feces were determined by methods described for the
grazing studies.
Samples of ruminal liquid were thawed and centrifuged at
30,090 X g for 20 min. The supematant was decanted for subsequent Co analysis. Samples of ruminal particulates were prepared
for Yb analysis according to the methods described by Ellis et al.
(1980). Concentrations of Co and Yb were determined using a
Perkin-Elmer model 2380 atomic absorption spectra-photometer
(Perkin-Elmer 1971). The natural log of Co or Yb concentration
was regressed on hour post-dosing to determine rates of fluid or
particulate outflow from the rumen (Grovum and Williams 1973).
Ruminal liquid volume was calculated from predicted initial concentration of Co and amount of Co pulsedosed into the rumen.
Ruminal particulate mass was calculated from predicted initial Yb
concentration and actual Yb dosage. Particulate mass flowing
from the rumen was calculated as the product of ruminal particulate passage rate and ruminal particulate mass (Grovum and Williams 1973). Content of IADF in feed, abomasal, and fecal samples
was used as an internal marker to determine digestibility coefticients. Digestibilities in the rumen, lower tract, and total tract were
calculated according to Harris (1970). In situ rate and extent of
NDF digestion, and discrete lag time were determined by fitting the
model of Mertens and Loften (1980).
Statisticd
Analysis
Grazing Trials
Esophageal masticate composition and in vivo organic matter
digestibility were analyzed with split block or repeated measures
designs (Gill and Hafs 1971, Steel and Torrie 1980). The model
included effects of animal, period, day, and the 2 and 3 way
interactions. Animal by period was the error term for animal and
period. Animal by period by day was the error term for day and the
2 way interactions with day. Linear and quadratic orthogonal
contrasts were calculated for period. Standing crop mass and
composition were analyzed with the previously described repeated
measures designs. Linear and quadratic orthogonal contrasts were
calculated for period. Regression equations were calculated to
relate diet quality and in vivo OMD with day of grazing. Additional
476
equations were calculated to relate diet quality with standing crop
composition.
Digestion Trial
Data were analyzed as a 4 X 4 Latin square (Steel and Torrie
1980). Linear and quadratic
maturity were calculated.
orthogonal
contrasts
for forage
Ramlts and Discussion
Grazing Trials
Numbers of animal-units (AU) per grazing treatment calculated
according to Scarnecchia and Gaskins (1987) were 2.9 and 3.2 for
the beginning and end of the 1985 study and 3.1 and 3.4 for the
beginning and end of the 1986 study. Grazing pressures for the
SDGsubunitsrangedfrom5.5
to20and6.7 to 19AU/torifor 1985
and 1986, respectively. Grazing pressures for the continuous unit
ranged from .9 to 3.5 and 1.0 to 1.63 AU/ton for 1985 and 1986,
respectively. Mean stocking density, calculated from mean animal
weight, for SDG subunits ranged from 7.4 to 10.5 and 6.6 to 10.6
AU/ha for 1985 and 1986, respectively. Stocking density for the
continuous unit ranged from .8 to .85 and .9 to .% AU/ ha for 1985
and 1986, respectively. System stocking levels were 2.7,2.8,2.0,2.2
AUM/ha for the SDG unit in 1985 and 1986 and the continuous
unit in 1985 and 1986, respectively.
Pasture forage (Table 1) under both grazing systems contained
similar crude protein (CP) content both years. However, in vitro
organic matter disappearance (IVOMD) was greater in 1986 than
1985 for both grazing systems. Pasture forage CP and IVOMD
under both grazing systems and standing crop under SDG declined
linearly across period.
A primary objective was to identify interactions of period with
subunits or days within period. These interactions were expected
due to reduced selective grazing across days within an SDG subunit and the possibility of differential effects of a grazing system
across period on plant regrowth. Diet chemical composition of
steers under SDG in 1985 (Table 2) was not affected by subunit
within period. Therefore, no differences due to subunit were
detected, Diet CP and IVOMD declined; NDF and ADF increased
across period as the plants matured.
In 1986, diet IVOMD of steers under SDG (Table 3) decreased
across day within subunit and period. Diet NDF and ADF
increased across day within subunit. This indicated that degree of
selective grazing was altered across day within subunit as grazing
JOURNAL
OF RANGE MANAGEMENT 42(6), November 1989
Table 3. Compodtloa of steer d&u (esophageal masticate) umler sbortduration and cootimwa
-Period
29
Item
fiY
1
-Period
30
31
MaY
MaY
22
JUn
grazhg, WM.
-Period
2
23
JUll
24
JUU
b
16
Jul
;:
;:
SEW
$bof OrganicMatter
Shortduration grazing
crude protein
In vitro OM digestibilityi’C
Neutral detergenttibef
Acid detergentfit&t
Acid detergentlignin
18.6
74.5
63.7
35.3
5.6
18.0
71.1
72.1
39.2
5.3
continuous glazing
crude protein
In vitro OM digestibility’
Neutral detergenttlber
Acid detergentfiber
Acid detergentligninb
17.2
75.9
60.5
32.8
3.3
15.3
77.8
59.7
33.4
3.3
17.4
z:
36:0
5.0
13.7
73.0
55.7
30.6
4.0
20.8
67.2
65.2
30.2
6.4
11.0
65.1
79.9
43.5
6.2
16.9
60.7
66.0
33.0
6.4
9.1
65.8
76.3
40.2
7.0
11.6
52.4
74.2
41.7
5.8
4.2
5.7
9.8
3.7
.9
16.3
75.7
64.6
35.5
4.0
13.2
73.5
60.8
34.1
5.0
18.0
57.0
61.7
37.1
6.3
15.5
60.2
65.8
38.4
5.5
11.5
58.6
71.8
40.9
6.5
9.8
9.4
62 1
66’2
35:5
5.1
3.9
2.9
5.2
2.5
1.1
z.3
34:0
5.5
%tandard error of the mean calculated from steer by period by dar. n = 2.
bLinear effect of period (Iy.10).
%ncar &cct of day (K.10).
kinr.ar effect of day (K.05).
-Period by day interaction (K.05).
under SDG reduced the availability of the preferred plant parts.
Chemical composition of steer diets under continuous graxing in
1985 (Table 2) was not affected by day within period similar to
steers under SDG. Esophageal masticate CP and IVOMD declined
and ADF increased across period as the piants matured.
In 1986, diet ADL of steers under continuous grazing (Table 3)
increased across period. An exception to the general trend was an
increase in IVOMD on day 2 of period 3. No effects of day within
period were detected for diet CP, NDF, or ADF, which indicated
that degree of selective grazing was not altered across the 3 sampling days in a period under continuous grazing.
A quadratic period by year interaction was detected for in vivo
organic matter digestibility by heifers under SDG (Table 4). This
Table 4. In vlvo organic matter dl@lblllty ollntermedlate whatgram by
bdfera under abort duration or continuom grazing.
G=iW
Management
Year
1986
1985
Period
PCriod
1
2
3
1
2
3
24-25 17-18 11-12 29-30 22-23 16-17
May Jun Jul May Jun Jul SE’
Short durationb
Continuousc
-lo viva organicmatterdigestibility,%66.4 71.0 58.8 70.0 61.0 54.3
63.5 60.5 51.7 64.9 59.0 51.0
2.0
1.3
%tanda~crro~of the mea! calc+ed from period by heifer (year) for n = 5.
bQ$.ad=d~~~~&y~~~~~)tion
(cU.05).
. .
interaction was apparently due to increased digestibility in period 2
of 1985. However, standing crop IVOMD~in 1985 showed only a
small reduction from period 1 to 2, which may indicate that standing crop measurements were not good single point predictors of in
vivo measurements. In vivo organic matter digestibiity (OMD) of
heifers under continuous grazing decrease d across period from
64.2 to 51.4% similar to standing crop and esophageal masticate
IVOMD.
Chemical composition of esophageal masticate is a result of the
interaction between chemical composition of forage and selection
by the animal. The quantity of forage present can affect diet
selection and intake by animals (Hodgson 1981). In 1985, total
JOURNAL OF RANGE MANAGEMENT 42(6), November 1989
herbage available per treatment in period 2 (Table 1) was similar
between grazing units. However, standing crop (g/m*) appeared
greater in the SDG subunits, which may have provided a greater
chance for selectivity.
Significant differences across days in period 1 would not be
expected since animals in both graxing systems were graxing homogeneous new pastures. By period 2, regrowth effects allowed
expression of differences in plant parts and chemical composition
of forage caused by differences in grazing. By period 3, standing
crop averaged only 1,549 kg/treatment in 1985 (Table 1); mostly
stem remained in both grazing treatments and the homogeneous
forage offered little opportunity for selective grazing.
The decline in CP content of esophageal masticate across periods was consistent with repotted values (Sims et al. 1971, Karnstra
1973, Rauzi 1975, Svejcar and Vavra 1985). There is wide variation
reported for IVOMD of forage varying in maturity, although
values reported by Svejcar and Vavra (1985) and White (1983) were
similar to the IVOMD of esophageal masticate collected in the
present study. Further, Pitts and Bryant (1987) and Taylor et al.
(1980) in Texas reported similar rates of change in esophageal
masticate contents of CP and IVOMD across collection date under
SDG, continuous, or Merrill grazing systems, as in the present
study. Greatest differences between in vivo OM digestibiities and
IVOMD occurred in periods 1 and 3 with IVOMD being higher in
both periods. The lower in vivo OM digestibility in period 1 could
have been due to a faster rate of particulate passage which would
have reduced in vivo OM digestibility. Increased NDF, ADF, and
ADL in esophageal masticate across periods was consistent with
reported values (Kamstra 1973, Cogwell and Kamstra 1976, Hart
et al. 1983).
Heifer average daily gain under SDG averaged .68 and .89 kg/d
in 1985 and 1986, respectively. Heifer average daily gain under
continuous grazing averaged .63 and .83 kg/d in 1985 and 1986,
respectively.
Digestion Trial
Forage crude protein content declined and forage NDF and
ADF content increased with increased forage maturity (Table 5).
Forage ADL was not affected by forage maturity. The decline of
CP with increased maturity of forage was greater for this study
than the CP decline reported by Sims et al. (1971), Kamstra (1973),
and Svejcar and Vavra (1985).
Organic matter intake by wethers and digestion coeffkients for
477
TM!&
RfktOfWtdQd
hwmedfate
wheatgraw (barvat date) on compaltlon oforgank
mattmend vohmtary
Intake, dlgdbmy,
ntwtml
detcrlcdfearkiodka,andramidpaaa~Linakrofwcthn.
Harvest date
Item
13Jul
6 Aug
72.5
7.1
422
5.3
7::
4414
6.3
7::;
43.0
6.4
747.2
64.2
563.2
z
447.0
58.5
55.9
2.5
65.0
62.7
83.8
33
2:o
1.2
1.8
26 May
19Jun
70.1
10.5
41.4
4.2
973.2
70.5
SEW
Composition, % of organic matter
crude protein’
Neutral
datargent fibar (NDF)*
Acid detergent f&r (ADF)’
Acid detergent lignin (ADL)
Intake and digestibility by w&era
Organic matter (OM) intaka, g/day”
OM digeatibiity, sbb
ADF
NDF diitibiity,
digestibiity, 96”
%’
Nitrogen digaatibiity, %
::
0.43
1.03
76.2
75.4
83.2
E
rro.1
66:7
81.8
In situ forage NDF kin&u in wethem
Digestion la& houra
Rata of NDF disaPPaarance, %/ hourC
Extant of NDF disappeerancc, %”
-0.t
4.7
82.8
0.07
4.4
75.5
:*:
69:o
2:;
::3
Ruminal Passage rate kin&Y of wathern
Ruminal liquid volume, liters
Ruminal liquid Passage, rata, %/bout)’
RttmiMlp#iCtdatamall~kg
Ruminal particulate pamage rate, /hour
Particulate mass outflow. n/ho 3
2.8
8.2
1.5
4.8
65.8
3.3
7.5
1.7
4.1
57.7
3.3
5.9
1.2
3.9
45.8
3.2
5.2
1.5
2.7
39.8
0.2
0.7
0.2
1.1
11.5
%andud crfor ofthe for n=4.
bLinarcffectofhawestdate(F<.10).
ziuar effectof llalvat date(X.05).
‘Liacardiea of lluvat date (K.01).
‘oUdratic c&t of harvcltdate(X.10).
Table 6. Ragradon aquatlona predktlog maymith
~aopbycrl~teof~~~rbo~d~toaladeoafiew~pulnltnw&yd~l.
YC8r
1985
Itam.
Equation
Short-duration grazing
CP = 14.52 -.10 Day
IVOMD = 75.18 - 23 Day
NDF = 49.88 + .I4 Day
ADF =28.09+.15Day
ADL = 5.24 + .06 Day
Continuous grazing
CP = 14.42 - .13 Day
IVOMD = 72.94 - .29 Day
NDF = 53.95 + .13Day
ADF = 29.52 + .14Day
ADL = 7.40 + .03 Day
1986
Root
MSE
P
20
.84
4.06
2.85
3.59
2.67
.004
.053
.071
.120
.380
CP
IVOMD
NDF
ADF
ADL
90
.74
.ll
48
.16
1.02
4.07
8.88
3.49
1.50
:g
.526
.125
,434
CP
IVOMD
NDF
ADF
ADL
rr
.89
.65
:Z
rr
Root
MSE
P
= 18.87 - .ll Day
= 74.62 - 25 Day
= 65.64 + . 10 Day
= 35.66 + .03 Day
= 5.01+ .02 Day
.61
.72
.19
.03
23
2.17
3.74
4.98
4.0
1.0
:g
.392
.732
.334
= 18.02 - .I2 Day
= 76.89 - 30 Day
= 60.53 + .09 Day
= 33.79 + .06 Day
= 3.49 + .05 Day
.52
69
::
2.87
4.76
10.46
6.85
.83
.105
.041
.701
692
.058
Equation
.63
‘CP = crudeprotein.IVOMD = in vitro organic matter diippmrame, NDF = neutral detergentfiber, ADF = acid detergentfiber, ADL =acid detergentIi.@.
OM, NDF, and ADF decmascd with increased forage maturity.
Post-ruminal digestion coefIlcients (calculated by difference) were
not affected by forage maturity and averaged .8,1.5, and 3.1% for
OM, NDF, and ADF, respectively. Additionally, in situ rate and
extent of NDF digestion, rate of liquid passage and particulate
mass outtlow from the rumen decreased with increased forage
maturity. Rate of particulate passage tended to decrease with
increased forage maturity.
Regmdon Rela~mhipa
In the graxing trials, rate of decline (Table 6) in diet CP across
days of grazing ranged from .lO to .13 percentage units/d. Diet
IVOMD declined from .23 to 30 percentage units/d across days of
grazing. Regression equations predicting forage CP and OM digestibility by wethers from harvest day after initiation of the graxing
trial were Forage CP, % q 10.23 - .08 Day (r2 = .88, PC.001) and
478
OM digestibility, % = 69.75 - .15 Day (rr =, PC.05). Forage NDF,
ADF, and ADL regressions were not signifiint and no regmssions
were improved by fitting quadratic regression lines. In vivo OMD
relationships, under SDG, were OMD, % = 61.14 + .78 Day - .02
Day2 (rr = .72, KOOl) and OMD, 9%= 71.91 - .32 Day (rr = 64,
F<.OOl) for 1985 and 1986, respectively. Under continuous graxing
the relationships derived were OMD, $ = 66.41- 24 Day (r2 = .72,
K.0001) and OMD, $ = 67.61 - .29 Day (rr = .77, K.0001).
Differences in potential prediction equations between studies arc
likely due to differences in animal species, amount of diet eelectivity allowed, and forage conservation.
Diet CP and IVOMD content could be adequately predicted
from pasture composition. In 1985 under SDG, the relationships
derived were Diet CP, %b=3.65 + 1.21 Pasture CP(r2= .89, X.01)
and Diet IVOMD, % = 1.51+ .92 Pasture IVOMD (rr = .70, K.05).
JOURNAL OF RANGE MANAGEMENT 42(6). November lB6B
In 1986, relationships under SDG were Diet CP, $ = 8.45 + 1.04
Pasture CP (r* = .61, PC. 1) and Diet IVOMD, $ = 1.21 Pasture CP
- 12.09 (r* = .72, X.05). In 1985 under continuous graxing, the
relationships derived were Diet CP, % = 2.80 + 1.18 Pasture CP (rr =
90, X.01) and Diet IVOMD, % = 1.91 Pasture IVOMD - 75.53
(r* = .82, X.01). In 1986, relationships under continuous grazing
were Diet CP, % = 8.44 + .89 Pasture CP (r2 = .41, X.2) and Diet
IVOMD, % = 2.89 Pasture IVOMD - 111.88 (r2 = .73, K.05).
Summary
This study involved 3 trials designed to assess the effects of
graxing system and plant maturity on animal and plant responses.
In this study, forage quality declined with increased maturity as
evidenced by decmased CP and increased fiber fraction contents.
In the grazing trials, this decrease in forage quality resulted in
decreased quality of forage consumed by animals. In vivo and in
vitro digestibility also decreased with increased forage maturity. In
the digestion trial, rate and extent of ruminal NDF digestion
declined with increased forage maturity. Poppi (1980) suggested
that decreased extent of digestion led to decreased rate of passage
and a subsequent decrease in intake. This suggestion is supported
by data from the digestion trial in which intake and particulate
mass flowing from the rumen declined significantly with increased
forage maturity.
Grazing systems have been used in attempts to alter chemical
composition of plants and, ultimately, intake by ruminants.
Although statistical comparisons were not appropriate, these data
suggest that effects of maturity were similar under SDG or continuous grazing. It is likely that variables more fundamental than the
choice of grazing system are more important in determining seasonal change in forage and diet quality and animal production.
Therefore, numerous field studies are needed to develop and validate sound empirical and/or theoretical models of the effects of
grazing management on seasonal changes in forage and diet quality and animal production.
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